The importance of gallium nitride (GaN) and related wide bandgap nitrides in the successful fabrication of light emitting diodes and semiconductor lasers has prompted considerable research into their growth and development as described in Strite et al., J. Vac. Sci. Technol.B 10:1237, 1992; Nakamura et al., Jpn. J. Appl. Phys. 34:L797, 1995; Jones et al., Chem. Vap. Deposition 65, 1995. The concept of single source compounds containing the N.sub.3 group has been extensively applied in recent years both in the US and Europe to prepare bulk powder and thin film material exhibiting interesting optical properties such as blue shifted light emissions.
Currently, the most common route to deposition of GaN by chemical vapor deposition (CVD) employs reactions of (CH.sub.3).sub.3 Ga and (C.sub.2 H.sub.5).sub.3 Ga with large excess of ammonia at temperatures in excess of 1000.degree. C. as described in Neumayer et al., Chem. Mater. 8:9, 1996. The high thermal stability of the N--H bond in NH.sub.3 necessitates deposition at extremely high temperatures.
Other azide-containing compounds that have been utilized to deposit GaN films contain organic groups. Unfortunately, the use of such compounds in many cases lead to unintentional incorporation of carbon impurities as described in Lakhoita et al., J. Chem. Mater. 3:441, 1995; Newmayer et al., J. Am. Chem. Soc. 117:5893, 1995; Muehr et al., Organometallics 15:2053, 1996.
A precursor of simplicity and low formula weight which has been used to generate GaN films is the well known H.sub.2 GaNH.sub.2 compound as described in Hwang et al., Chem. Mater. 7:517(1995). However, this material is polymeric in the solid state and thus unsuitable for GaN film growth. Furthermore, it has been established that the extremely stable N--H bonds in the compound facilitate loss of NH.sub.3 during its thermal decomposition to yield non-stoichiometric nitride material of composition GaN.sub.0.83.
Other precursor compounds which have been used to generate gallium nitride films include diethylgallium azide as described in Kouvatekis et al., Chem. Mater. 1:476-478, 1989; Atwood et al., J. Organomet. Chem. 394:C6-C8, 1990; Lakhotia et al., Chem. Mater. 7:546-552, 1995; gallium imide as described in Janik et al., Chem. Mater. 8:2708-2711, 1996; and cyclotrigallazane as described in Hwang et al., Chem. Mater 7:517-525, 1995; Jegler et al., Chem Mater. 10:2041-2043, 1998.
Previous studies as reported in Kouvetakis et al., Inorg. Chem 36:1792, 1997; Kouvetakis et al., Chem. of Mat. 1:476, 1989, both incorporated by reference herein have demonstrated that the decomposition of an exclusively inorganic precursor, Cl.sub.2 GaN.sub.3, leads to thin, oriented GaN layers on (100) Si substrates and heteroepitaxial films on basal plane sapphire at 700.degree. C. The probable decomposition pathway for this precursor is demonstrated by the following equation: EQU (Cl.sub.2 GaN.sub.3).sub.3.fwdarw.GaN+2GaCl.sub.3 +4N.sub.2.
The development of this compound demonstrated that a single source inorganic precursor could lead to the formation of single-crystalline GaN at low temperatures and at exceptionally high growth rates by conventional low-pressure deposition techniques as described in McMurran et al., App. Phys. Lett. 69:203-205, 1996, incorporated by reference herein.
Alternative synthetic methods based on single source molecular precursors that incorporate direct Ga--N bonds and labile, preferably, non-organic leaving groups offer the potential of significant improvements in film quality and growth process. Some of these benefits include lower deposition temperature, elimination of the inefficient use of ammonia, reduction in nitrogen vacancies and carbon contamination, and much enhanced doping capabilities.
It is desirable that optimal precursor compounds provide a facile decomposition pathway leading to the desirable material and be sufficiently volatile at room temperature to be applicable for chemical vapor deposition (CVD) or molecular beam epitaxy (MBE). However, most reported single source precursors are polynuclear species with very low vapor pressure which makes them unsuitable, or at best makes their use inconvenient, for CVD.